JP5510311B2 - Heating resistance type flow sensor and its self-diagnosis method - Google Patents

Description

  The present invention relates to a heating resistance type flow sensor and a self-diagnosis method thereof.

  Conventionally, for example, a configuration shown in Patent Document 1 has been proposed as a heating resistance type flow sensor.

  In Patent Document 1, when the self-diagnosis start signal DAIG is input, the operation of the heater control circuit stops, and thereby the output of the air flow meter changes to the zero point output of the temperature difference bridge signal. Here, the zero point output is a state in which no heater current flows (a state in which the heater current is not heated), and a state in which intake air does not flow because the engine is in a stopped state.

  Then, the control unit samples the zero point voltage, calculates the amount of deviation from the initial zero point, and determines that it is a failure when the amount of deviation is abnormally large (paragraph [0019] of Patent Document 1). -See [0021]).

JP-A-3-33619

  As described above, in Patent Document 1, the circuit (in particular, the temperature difference bridge circuit) can be self-diagnosis only in a state where the heater current does not flow and the intake air does not flow.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a heating resistance flow sensor capable of determining whether a circuit is normal or abnormal regardless of whether or not a fluid is flowing, and a self-diagnosis method thereof.

In order to achieve the above object, the invention described in claim 1
A heater resistor (11) formed on the substrate (60) and generating heat when energized;
A heater drive unit (12) for controlling the energization state of the heater resistor (11);
Two first flow rate detection resistors (30u, 30d) are formed on the substrate (60) in the same pattern using the same material and are located at an equal distance on the upstream side and the downstream side with respect to the heater resistor (11). A first flow rate detection resistor pair (30) connected in series with each other;
The same material as the first flow rate detection resistors (30u, 30d) is used to form the same pattern on the substrate (60), and the heater resistance (11) is formed at a different distance from the first flow rate detection resistors (30u, 30d). On the other hand, two second flow rate detection resistors (31u, 31d) positioned equidistantly on the upstream side and the downstream side are connected in series to each other and connected in parallel to the first flow rate detection resistor pair (30). A second flow rate detection resistor pair (31);
An external output terminal (16b),
During normal operation for detecting the flow rate of the fluid, a signal based on the output of the first bridge circuit (38) constituted by the two flow rate detection resistor pairs (30, 31) is externally supplied via the external output terminal (16b). A heating resistance flow sensor (10) that outputs to
The same material as the flow rate detection resistors (30u, 30d, 31u, 31d) is formed on the substrate (60) in the same pattern, and is positioned at different distances on the upstream side and the downstream side with respect to the heater resistor (11). Two self-diagnostic resistors (32u, 32d) are connected in series to each other, and a self-diagnostic resistor pair (32) is connected in parallel to the two flow rate detecting resistor pairs (30, 31).
Of the three resistance pairs (30, 31, 32), a first bridge circuit (38) constituted by two flow rate detection resistance pairs (30, 31), and a first flow rate detection resistance pair (30) First selection means (33) for selectively connecting any one of the second bridge circuits (39) constituted by the self-diagnosis resistor pair (32) to the external output terminal (16b);
During a predetermined first period (t1) that does not overlap with that during normal operation, the heater drive unit (12) cuts off the power supply to the heater resistor (11), and the first selection circuit (33) uses the first bridge circuit. (38) is connected to the external output terminal (16b),
During normal operation and in a second period (t2) that does not overlap with the first period, power is supplied to the heater resistor (11) by the heater drive section (12) and the second bridge circuit is supplied by the first selection means (33). (39) is connected to the external output terminal (16b).

  In the present invention, in the first period (t1), the first bridge circuit (38) composed of the flow rate detection resistor pair (30, 31) located at the same distance from the heater resistor (11) is selected, and the heater resistance No current flows through (11) and the heater resistance (11) does not generate heat. For this reason, the temperature on the substrate (60) becomes uniform, and the resistance values of all the flow rate detection resistors (30u, 30d, 31u, 31d) constituting the first bridge circuit (38) become equal. Accordingly, the output of the first bridge circuit (38) is in a state where the flow rate is set to 0 in a pseudo manner regardless of whether or not the fluid is flowing (for example, regardless of whether the engine is rotated or stopped).

  On the other hand, in the second period (t2), the second bridge circuit (39) including the self-diagnosis resistor pair (32) located at a different distance from the heater resistor (11) is selected, and the heater resistor (11) is selected. Electric power is supplied, and the heater resistor (11) generates heat. When the heater resistance (11) generates heat, the temperature on the substrate (60) has a maximum temperature in the heater resistance (11) and a temperature gradient occurs in the fluid flow direction. However, since the upstream self-diagnosis resistor (32u) and the downstream self-diagnosis resistor (32d) constituting the self-diagnosis resistor pair (32) are different in distance from the heater resistor (11), the temperature thereof As a result, the resistance value is also different. Therefore, the output of the second bridge circuit (39) is in a state where the flow rate is not equal to 0 even if no fluid is flowing (for example, even when the engine is stopped).

  Thus, according to the present invention, it is possible to create a state where the flow rate = 0 and a state where the flow rate ≠ 0 regardless of whether or not the fluid is flowing. Therefore, it is possible to determine whether the circuit is normal or abnormal based on the outputs of the two states.

As claimed in claim 2,
A first differential amplifier (34) having a connection point (35) of the first flow rate detection resistor (30u, 30d) connected to one of the input terminals, and an output terminal electrically connected to the external output terminal (16b). With
The first selection means (33) connects the connection point (36) of the second flow rate detection resistors (31u, 31d) during the normal operation and the first period (t1) to the input terminal of the first differential amplifier (34). In the second period (t2), the connection point (37) of the self-diagnosis resistors (32u, 32d) can be connected to the input terminal of the first differential amplifier (34). .

  According to this, in the normal operation and in the first period (t1), the potential difference at each connection point (35, 36) in the first bridge circuit (38) is output from the first differential amplifier (34), and the second In the period (t2), the potential difference at each connection point (35, 37) of the second bridge circuit (39) can be output from the first differential amplifier (34).

Specifically, as described in claim 3,
The heater drive unit (12)
The two first fixed resistors (21a, 21b) formed on the substrate (60) and connected in series to each other are formed on the substrate (60) and receive the heat of the heater resistor (11) to change the resistance value. A thermal resistance (20) is connected in series and formed on the substrate (60), and a fluid temperature measurement resistor (22) whose resistance value changes according to the temperature of the fluid, and a second fixed resistor ( 23) a third bridge circuit (27) connected in series;
The connection point (29) of the fluid temperature measurement resistor (22) and the second fixed resistor (23) is connected to one of the input ends, and the side heat resistance (20) and the first fixed resistor (21a) are connected to the other input end. A second differential amplifier (25) to which a connection point (28a) or a connection point (28b) between two first fixed resistors (21a, 21b) is connected;
Second selection means (24) for selectively connecting one of the two connection points (28a, 28b) to the input terminal of the second differential amplifier (25);
A transistor (26) connected to the output terminal of the second differential amplifier (25) and controlling the energization state of the heater resistor (11) based on the output of the second differential amplifier (25);
The second selection means (24) connects the connection point (28b) between the two first fixed resistors (21a, 21b) to the input terminal of the second differential amplifier (25) in the first period (t1). In the normal operation and in the second period (t2), the connection point (28a) of the indirectly heated resistor (20) and the first fixed resistor (21a) is connected to the input terminal of the second differential amplifier (25). According to this, from the relationship between each potential of the two connection points (28a, 28b) on the side heat resistance (20) side and the potential of the connection point (29) on the fluid temperature measurement resistance (22) side In the first period (t1), no current flows through the heater resistor (11), and in the second period (t2), a current flows through the heater resistor (11).

As claimed in claim 4,
As a self-diagnosis means,
A power-on reset circuit (50 connected to a power supply line from the power supply terminal (16a) to the transistor (26) and outputs a power-on reset signal for initializing the circuit when power is supplied to the power supply terminal (16a). )When,
In the first period (t1) based on the power-on reset signal, the first selection means (33) connects the connection point (36) of the second flow rate detection resistors (31u, 31d) to the first differential amplifier (34). And the second selection means (24) connects the connection point (28b) of the first fixed resistors (21a, 21b) to the input terminal of the second differential amplifier (25),
In the second period (t2) based on the power-on reset signal, the first selection means (33) inputs the connection point (37) of the self-diagnosis resistors (32u, 32d) to the first differential amplifier (34). The second selection means (24) connects the connection point (28a) of the first fixed resistor (21a) and the indirectly heated resistor (20) to the input end of the second differential amplifier (25) while being connected to the end. In addition,
And a selection means control circuit (51) for controlling the two selection means (24, 33).

  According to this, the state of the first period (t1) and the state of the second period (t2) are changed to the heating resistance with the power supply to the heating resistance type flow sensor (10) via the power terminal (16a) as a trigger. A type flow sensor (10) can be formed. Thereby, the self-diagnosis terminal (16e) can be made unnecessary. For this reason, cost reduction and size reduction can be achieved.

  As described in claim 5, when the power-on reset signal is input, the selection means control circuit (51) controls the two selection means (24, 33) in the state of the first period (t1), When the first period (t1) ends, the two selection means (24, 33) may be controlled to be in the second period (t2) after the first period (t1).

  According to this, since the first period (t1) in which the heater resistor (11) does not generate heat first is set, compared to the configuration in which the second period (t2) in which the heater resistor (11) generates heat does not decrease, first. Self-diagnosis time can be shortened.

  As described in claim 6, the self-diagnosis resistors (32u, 32d) are more resistant to the heater resistance (11) than the first flow rate detection resistors (30u, 30d) and the second flow rate detection resistors (31u, 31d). It is good to set it as the structure formed in the position far from. In addition, as described in claim 7, the self-diagnosis resistor (32u, 32d) is provided between the first flow rate detection resistor (30u, 30d) and the second flow rate detection resistor (31u, 31d). Or a self-diagnosis resistor (32u, 32d) comprising a first flow rate detection resistor (30u, 30d) and a second flow rate detection resistor (31u, 31d). It can also be set as the structure formed in the position nearer to heater resistance (11) than.

  In particular, when the configuration according to claim 6 is adopted, compared to the other configurations, the formation region of the resistors (30u, 30d, 31u, 31d, 32u, 32d) constituting the two bridge circuits (38, 39), and thus The physique of the heating resistance flow sensor (10) can be reduced in size. Further, the heater resistor (11) and the resistor (30u, 30d, 31u, 31d) constituting the first bridge circuit (38) used during normal operation (flow rate detection) generate a considerable amount of heat due to energization. Since there is no self-diagnosis resistor (32u, 32d), the accuracy of flow rate detection can be improved.

As claimed in claim 9, comprising a self-diagnosis terminal (16e),
Based on the self-diagnosis instruction signal input from the outside through the self-diagnosis terminal (16e),
In the first period (t1), the heater drive section (12) cuts off the power supply to the heater resistor (11), and the first selection circuit (33) connects the first bridge circuit (38) to the external output terminal ( 16b),
In the second period (t2), electric power is supplied to the heater resistor (11) by the heater driving section (12), and the second bridge circuit (39) is connected to the external output terminal (16b) by the first selection means (33). It is also possible to adopt a configuration connected to the.

  As described above, based on the self-diagnosis instruction signal input from the self-diagnosis terminal (16e), the energization state of the heater resistor (11) and the bridge circuit (38, 39) by the first selection means (33). Even if the selection is controlled, it is possible to create a state where the flow rate = 0 and a state where the flow rate ≠ 0 regardless of whether or not the fluid is flowing. Therefore, it is possible to determine whether the circuit is normal or abnormal based on the output of each state.

Next, the self-diagnosis method of the heating resistance type flow sensor according to claim 10 is:
The heating resistance flow sensor (10) according to any one of claims 1 to 9, wherein the output of the external output terminal (16b) in the first period (t1) and the external output terminal (16b) in the second period (t2). The self-diagnosis is performed based on the difference between the outputs.

  As described above, in the first period (t1), a state where the flow rate = 0 is created in a pseudo manner, and in the second period (t2), a state where the flow rate is not equal to 0 is created. Therefore, by taking the difference between the outputs in the two periods (t1, t2), it is possible to self-diagnose whether the circuit constituting the heating resistance flow sensor (10) is normal or abnormal.

It is a circuit diagram which shows schematic structure of the heating resistance type flow sensor which concerns on 1st Embodiment. The sensor chip | tip of the heating resistance type | mold flow sensor shown in FIG. 2 is shown, (a) is a top view, (b) is sectional drawing which follows the IIb-IIb line | wire of (a). 2 is a timing chart showing a self-diagnosis procedure in the heating resistance flow sensor shown in FIG. 1. It is a circuit diagram which shows schematic structure of a modification. It is a circuit diagram which shows schematic structure of the heating resistance type flow sensor which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, common or related elements are given the same reference numerals.

(First embodiment)
The heating resistance type flow rate sensor according to the present embodiment detects the flow rate of the fluid by utilizing heat transfer with the fluid. For example, an air flow (intake air) sucked into an internal combustion engine (not shown) of the vehicle. In order to detect the flow rate of the flow).

  In addition, the heating resistance type flow sensor has a detection flow path (not shown) for taking a part of the intake air flow for detecting the flow rate, and disposed in the detection flow path. A heater resistor that generates heat when energized is provided. Then, a temperature distribution is formed in the flow direction of the intake air flow in the detection flow path due to the heat generated by the heater resistance, and a signal indicating the intake air amount is output from the external output terminal based on this temperature distribution.

  Then, a signal output from the heating resistance type flow sensor is input to, for example, an electronic control unit (ECU) for controlling the internal combustion engine, and the ECU grasps the intake air amount based on this signal and determines the intake air amount. Various control processes, such as fuel injection control based on it, are performed.

  As shown in FIG. 1, a heating resistance type flow sensor 10 includes a heater resistor 11, a heater drive unit 12 that controls driving of the heater resistor 11, a sensor unit 13 that outputs a signal corresponding to the flow rate based on a temperature distribution, and a sensor. The signal processing circuit unit 14 performs various processes on the signal output from the unit 13 and outputs the signal. The self-diagnosis circuit unit 15 switches the heater driving unit 12 and the sensor unit 13 to the self-diagnosis mode at a predetermined timing. The self-diagnosis circuit unit 15 corresponds to the self-diagnosis means described in the claims.

  The heater resistor 11 is a resistor that generates heat when energized. As shown in FIGS. 2A and 2B, the heater resistor 11 is provided on a membrane 61 formed on a substrate 60 (hereinafter referred to as a sensor chip 60) such as silicon. In the present embodiment, a flat rectangular sensor chip 60 is employed as shown in FIG. 2A, and the short direction of the sensor chip 60 (hereinafter simply referred to as the short direction) follows the flow of the fluid. It has become. The membrane 61 is formed on one end side in the longitudinal direction of the sensor chip 60 (hereinafter simply referred to as the longitudinal direction). In addition, the heater resistor 11 is disposed in the planar rectangular membrane 61 so as to extend in the longitudinal direction at the center position in the lateral direction.

  The heater driving unit 12 is a circuit that controls the heater resistance 11 to generate heat according to the flow rate so that the temperature of the heater resistance 11 becomes a reference temperature that is higher than the fluid temperature by a certain temperature. In the present embodiment, the heater driving unit 12 includes an indirectly heated resistor 20, first fixed resistors 21a and 21b, an intake air temperature measuring resistor 22, a second fixed resistor 23, a switch 24, an amplifier 25, and a heater resistor driving transistor 26. Have. Then, the energization state of the heater resistor 11 is controlled so that the temperature difference between the indirectly heated resistor 20 and the temperature measuring resistor 22 becomes constant.

  The intake air temperature measurement resistor 22 corresponds to the fluid temperature measurement resistor described in the claims. The switch 24 corresponds to a second selection unit described in the claims. The amplifier 25 corresponds to a second differential amplifier described in the claims.

  The indirectly heated resistor 20 is a resistor whose resistance value is changed by the heat of the heater resistor 11 being transmitted through a membrane 61 portion of the sensor chip 60 described later. On the other hand, the intake air temperature measurement resistor 22 is a resistor whose resistance value varies depending on the ambient temperature (fluid temperature). These side heat resistance 20, intake temperature measurement resistance 22, and fixed resistances 21 a, 21 b, and 23 are formed on the same sensor chip 60 as the heater resistance 11. The side heat resistor 20 is also formed in the membrane 61 in the vicinity of the heater resistor 11 and has a substantially U-shaped plane so as to sandwich the heater resistor 11 in the short direction. The intake air temperature measurement resistor 22 is not affected by the heat of the heater resistor 11 and is part of the sensor chip 60 excluding the membrane 61 (thermally separated from the membrane 61) so as to be in the same fluid condition as the heater resistor 11. And is formed at substantially the same position as the heater resistor 11 in the longitudinal direction and upstream of the membrane 61 in the short direction. The fixed resistors 21a, 21b, and 23 are thick portions excluding the membrane 61 of the sensor chip 60, and are formed at positions away from the membrane 61 in the longitudinal direction.

  In the present embodiment, the side heat resistance 20 and the intake air temperature measurement resistance 22 both have a positive temperature coefficient. In addition, the indirectly heated resistor 20 and the first fixed resistors 21a and 21b include the indirectly heated resistor 20 on the low potential side (ground potential side) and the two first fixed resistors 21a and 21b connected in series on the high potential side (internally constant). Are connected in series as the potential Vr side). The two first fixed resistors 21a and 21b are such that the first fixed resistor 21a is on the side heat resistor 20 side. On the other hand, the intake temperature measuring resistor 22 and the second fixed resistor 23 are connected in series with the intake temperature measuring resistor 22 as a low potential side (ground potential side) and the second fixed resistor 23 as a high potential side (internal constant potential Vr side). Has been. These constitute the bridge circuit 27. The bridge circuit 27 corresponds to a third bridge circuit described in the claims.

  In the bridge circuit 27, the connection point 28a between the indirectly heated resistor 20 and the first fixed resistor 21a is connected to the terminal 24a of the switch 24, and the connection point 28b of the first fixed resistors 21a and 21b is connected to the terminal 24b of the switch 24. Yes. One of the terminals 24 a and 24 b (connection points 28 a and 28 b) is connected to the inverting input terminal of the amplifier 25. On the other hand, the connection point 29 between the temperature measurement resistor 22 and the second fixed resistor 23 is directly connected to the non-inverting input terminal of the amplifier 25.

  The switch 24 connects the terminal 24 a (connection point 28 a) and the inverting input terminal of the amplifier 25 during normal operation (flow rate measurement). In the self-diagnosis described later, the terminal 24b (connection point 28b) and the inverting input terminal of the amplifier 25 are connected in the first period (t1), and the terminal 24a (connection point 28a) is connected in the second period (t2). The inverting input terminal of the amplifier 25 is connected.

  The amplifier 25 amplifies and outputs (differential amplifies) the difference (V2−V1) between the potential V1 input to the inverting input terminal and the potential V2 input to the non-inverting input terminal. The amplifier 25 includes a phase compensation capacitor (not shown).

  The transistor 26 is driven and controlled in accordance with the output of the amplifier 25, and thereby plays a role of flowing a current from the power supply voltage Vcc to the heater resistor 11. The transistor 26 passes a current having a magnitude corresponding to the output of the amplifier 25. In other words, the heater resistor 11 generates heat in accordance with the magnitude of the current passed by the transistor 26.

  In this embodiment, an npn-type bipolar transistor is employed as the transistor 26, the base is connected to the output terminal of the amplifier 25, the emitter is connected to the heater resistor 11, and the collector is connected to the power supply terminal 16a. . The transistor 26 passes a current having a magnitude corresponding to the output (base potential) of the amplifier 25 when the potential V2 is higher than the potential V1 (V2> V1).

  The resistance value Ri of the indirectly heated resistor 20, the resistance value Rk of the intake air temperature measuring resistor 22, the resistance values R1a and R1b of the fixed resistors 21a and 21b, and the resistance value R2 of the fixed resistor 23 are in a non-energized state (same temperature). Rk> Ri, V1> V2 in a first period t1, which will be described later, and at least V2> V1 immediately after switching in a second period t2.

  With the above configuration, the heater driving unit 12 controls the temperature of the heater resistor 11 to a reference temperature that is higher than the fluid temperature by a certain temperature. In other words, during normal operation, when the temperature of the heater resistor 11 falls below the reference temperature, the temperature of the indirectly heated resistor 20 also decreases and the resistance value Ri of the indirectly heated resistor 20 decreases, and the potential difference between the connection points 28a and 29 is reduced. The output of the signal starts from the amplifier 25 with the polarity reversed. As a result, the transistor 26 is actuated to energize the heater resistor 11, the temperature of the side heat resistor 20 increases with the temperature of the heater resistor 11, and the resistance value Ri of the side heat resistor 20 increases.

  As a result, the sign of the potential difference between the connection points 28a and 29 is reversed again, the output of the signal from the amplifier 25 is stopped, the transistor 26 stops operating, and the energization to the heater resistor 11 is stopped. Then, when the temperature of the heater resistor 11 decreases again below the reference temperature, the same operation is repeated.

  Next, the sensor unit 13 includes three half bridges 30, 31, 32, a switch 33, and an amplifier 34 formed by connecting resistors arranged on the upstream side and the downstream side of the heater resistor 11 in series. The half bridge 30 is a first flow rate detection resistor pair, the half bridge 31 is a second flow rate detection resistor pair, and the half bridge 32 is a claim. This corresponds to the third flow rate detection amount resistance pair described in the range. The switch 33 corresponds to the first selection means described in the claims. The amplifier 34 corresponds to a first differential amplifier described in the claims.

  The half bridge 30 is formed by connecting in series a first upstream flow rate detection resistor 30u and a first downstream flow rate detection resistor 30d that are arranged at an equal distance between the upstream side and the downstream side of the heater resistor 11. In the present embodiment, two resistors 30u and 30d are connected in series with the first upstream flow rate detection resistor 30u as a low potential side (ground potential side). These resistors (30u, 30d) correspond to the first flow rate detecting resistor described in the claims.

  The half bridge 31 has a second upstream flow rate detection resistor 31u and a second downstream side that are different from the resistances (30u, 30d) and are arranged at an equal distance between the upstream side and the downstream side of the heater resistor 11. A flow rate detection resistor 31d is connected in series. In the present embodiment, two resistors 31u and 31d are connected in series with the second downstream flow rate detection resistor 31d as a low potential side (ground potential side). These resistors (31u, 31d) correspond to a second flow rate detecting resistor described in the claims.

  On the other hand, the half bridge 32 has a different distance from the resistors 30u, 30d, 31u, 31d, and an upstream self-diagnosis resistor 32u and a downstream disposed at different distances on the upstream side and the downstream side of the heater resistor 11. A side self-diagnosis resistor 32d is connected in series. In the present embodiment, two resistors 32u and 32d are connected in series with the upstream self-diagnosis resistor 32u as a low potential side (ground potential side). These resistors (32u, 32d) correspond to the self-diagnosis resistors described in the claims.

  In these half bridge circuits 30, 31, and 32, a connection point 35 of the first flow rate detection resistors 30 u and 30 d constituting the half bridge circuit 30 is connected to the inverting input terminal of the amplifier 34. On the other hand, the connection point 36 of the second flow rate detection resistors 31u and 31d constituting the half-bridge circuit 31 is connected to the terminal 33a of the switch 33, and the connection point 37 of the self-diagnosis resistors 32u and 32d constituting the half-bridge circuit 32. Is connected to the terminal 33 b of the switch 33. One of the terminals 33 a and 33 b (connection points 36 and 37) is connected to the non-inverting input terminal of the amplifier 41.

  Each resistor 30u, 30d, 31u, 31d, 32u, 32d is formed in the same pattern shape using the same material. That is, both have the same temperature coefficient and the same resistance value at the same temperature. When the power supply terminal 16a is turned on, it is energized by receiving power from the internal power supply Vr. In this embodiment, it has a positive temperature coefficient. The resistors 30u, 30d, 31u, 31d, 32u, and 32d are formed on the membrane 61 of the same sensor chip 60 as the heater resistor 11, and are shown in FIG. 2A from the upstream side toward the downstream side. Thus, the upstream resistors 32u, 31u, 30u and the downstream resistors 30d, 31d, 32d are provided in this order.

  That is, in the resistors 30u, 30d, 31u, 31d, 32u, and 32d that constitute the sensor unit 13, the self-diagnosis resistors 32u and 32d that constitute the half bridge 32 are provided at positions farthest from the heater resistor 11. . As shown in FIG. 2A, the self-diagnosis resistors 32u and 32d are provided such that the upstream self-diagnosis resistor 32u is located farther from the heater resistor 11 than the downstream self-diagnosis resistor 32d. Yes. As described above, the self-diagnosis resistors 32u and 32d are different in distance from the heater resistor 11 and different in temperature when the heater resistor 11 generates heat.

  The switch 33 connects the terminal 33a (connection point 36) and the non-inverting input terminal of the amplifier 41 during normal operation (when measuring the flow rate), and during self-diagnosis, the terminal 33a (connection) The point 36) is connected to the non-inverting input terminal of the amplifier 41, and the terminal 33b (connection point 37) is connected to the non-inverting input terminal of the amplifier 41 in the second period t2.

  That is, in the first period t1 during the normal operation and the self-diagnosis, the bridge circuit 38 in which the half-bridge circuits 30 and 31 are connected in parallel is used, and in the second period t2 during the self-diagnosis, the half-bridge circuit 30 is used. , 32 are connected in parallel. The bridge circuit 38 corresponds to the first bridge circuit described in the claims, and the bridge circuit 39 corresponds to the second bridge circuit described in the claims.

  The amplifier 34 amplifies and outputs (differential amplifies) the difference (V4−V3) between the potential V3 input to the inverting input terminal and the potential V4 input to the non-inverting input terminal.

  With the above configuration, the sensor unit 13 outputs a voltage value corresponding to the intake air amount. A temperature distribution corresponding to the intake air amount is formed on the membrane 61 in the flow direction of the intake air flow by the heater resistor 12 controlled to the reference temperature by the heater driving unit 12. The resistance values of the upstream resistances 30u, 31u, and 32u and the downstream resistances 30d, 31d, and 32d are numerical values corresponding to the temperature distribution (that is, numerical values corresponding to the intake air amount).

  For this reason, for example, when the intake air amount increases and the temperature distribution is biased toward the downstream side, the temperature decreases on the upstream side of the heater resistor 11 and the resistance values of the upstream resistors 30u, 31u, 32u decrease, and the heater resistor 11 On the downstream side, the temperature rises and the resistance values of the downstream resistors 30d, 31d, and 32d increase.

  As a result, the potential difference between the connection points 35 and 36 changes, so that the sensor unit 13 (bridge circuit 38) can output the potential difference between the connection points 35 and 36 as a voltage value corresponding to the intake air amount. That is, the sensor unit 13 can output the resistance value changes of the upstream flow rate detection resistors 30u and 31u and the downstream flow rate detection resistors 30d and 31d as the intake air amount changes as the voltage value of the bridge circuit 38. .

  Next, the signal processing circuit unit 14 includes an A / D converter 40 that converts a signal output from the sensor unit 13 into a digital value, and a DSP (digital signal signal processor) that performs various arithmetic processes on the digitized voltage value. Processor) 41, a D / A converter 42 that converts a digital value output from the DSP 41 into an analog value and outputs the analog value to an external output terminal (Vout) 16b, a memory that stores various numerical values necessary for arithmetic processing by the DSP 41 43 etc. For example, the memory 43 stores the sensitivity of the heating resistor type flow sensor 10 (sensor unit 13), the offset adjustment value, the characteristic value at the time of shipment, and the like.

  In this embodiment, an example in which a digital value output from the DSP 41 is converted into an analog value and output to the external output terminal 16b is shown. However, instead of the D / A converter 42, the digital value is converted to the frequency of the pulse signal. It is also possible to employ a D / F converter that converts the signal into an output. Also, digital values can be output as they are.

  The self-diagnosis circuit unit 15 includes a power-on reset circuit 50 and a switch control circuit 51. The switch control circuit 51 corresponds to the selection means control circuit described in the claims.

  The power-on reset circuit 50 outputs a power-on reset signal each time the ignition key is turned on and the power supply Vcc is turned on to the power supply terminal 16 a of the heating resistance flow sensor 10, thereby configuring the heating resistance flow sensor 10. Initialize each circuit. For this reason, each circuit constituting the heating resistance flow sensor 10 is initialized by the power-on reset signal and then starts operating.

  The switch control circuit 51 uses the power-on reset signal as a trigger to connect the switch 24 to the terminal 24b (connection point 28b) and connect the switch 33 to the terminal 33a (connection point 36) in a predetermined first period t1. In addition, the operation of the switches 24 and 34 is controlled. Further, in a predetermined second period t2 different from the first period t1, the switches 24, 24 are connected so that the switch 24 is connected to the terminal 24a (connection point 28a) and the switch 33 is connected to the terminal 33b (connection point 37). 34 is controlled. In the present embodiment, the predetermined period from the start of the operation after being initialized by the power-on reset signal is defined as the first period t1, and after the end of the first period t1, the second period t2 is continued.

  Note that the switch 24, the amplifier 25, the transistor 26, the switch 33, the amplifier 34, the A / D converter 40, the DSP 41, the D / A converter 42, the memory 43, the power-on reset circuit 50, the switch control circuit 51, and the power supply terminal 16a. The external output terminal 16b, the ROM terminal 16c, the ground terminal 16d, and the like are mounted on a circuit chip 70 different from the sensor chip 60 provided with various resistors such as the heater resistor 11, and various resistors such as the heater resistor 11 are provided. They are electrically connected by bonding wires (not shown) or the like.

  Next, a self-diagnosis method in the heating resistance flow sensor 10 will be described with reference to FIG.

  As shown in FIG. 3, when the ignition key is turned on and the power supply Vcc is turned on to the power supply terminal 16a of the heating resistance flow sensor 10, the power-on reset circuit 50 outputs a power-on reset signal. With this power-on reset signal, each circuit constituting the heating resistance flow sensor 10 is initialized, and after this initialization, the operation is started. When the power supply Vcc is turned on to the power supply terminal 16a, the internal power supply Vr also rises.

  In a predetermined period (first period t1) after the initialization, the switch control circuit 51 connects the switch 24 to the terminal 24b (connection point 28b) and connects the switch 33 to the terminal 33a (connection point 36). Let

  When the connection point 28b is connected to the inverting input terminal of the amplifier 25, the potential V1 of the inverting input terminal of the amplifier 25 is derived from the relationship between the resistance values of the resistors 20, 21a, 21b, 22, 23 constituting the bridge circuit 27 described above. Becomes higher than the potential V2 of the non-inverting input terminal (V1> V2). Therefore, no output is made from the amplifier 25, the transistor 26 is turned off, and no current flows through the heater resistor 11.

  Accordingly, the temperature on the membrane 61 becomes uniform, and the flow rate detection resistors 30u, 30d, 31u, 31d constituting the bridge circuit 38 connected to the amplifier 34 all have the same resistance value. That is, there is no potential difference between the potential V3 at the inverting input terminal of the amplifier 34 and the potential V4 at the non-inverting input terminal (V3 = V4). For this reason, it is possible to forcibly (pseudo) creating a flow rate = 0 state regardless of whether the engine is rotated or stopped (regardless of whether or not the fluid is flowing).

  Therefore, the flow rate = 0 can be measured by measuring the output of the external output terminal 16b during the first period t1 (measurement A shown in FIG. 3).

  Next, after the first period t1, the switch control circuit 51 connects the switch 24 to the terminal 24a (connection point 28a) and the switch 33 to the terminal 33b (connection) in a predetermined period (second period t2). Connect to point 37).

  When the connection point 28 a is connected to the inverting input terminal of the amplifier 25, the potential of the non-inverting input terminal of the amplifier 25 is derived from the relationship between the resistance values of the resistors 20, 21 a, 21 b, 22, and 23 constituting the bridge circuit 27. V2 becomes larger than the potential V1 of the inverting input terminal (V2> V1). Accordingly, until V1 = V2, the transistor 26 is turned on, a current flows through the heater resistor 11, and the heater resistor 11 generates heat.

  Thus, when the heater resistor 11 generates heat, the heater resistor 11 has the maximum temperature on the membrane 61, and a temperature gradient is generated in the fluid flow direction. Here, since the upstream side self-diagnosis resistor 32u is disposed at a position farther from the heater resistor 11 than the downstream side self-diagnosis resistor 32d, the amount of heat transmitted from the heater resistor 11 is reduced to the downstream side self-diagnosis resistor. The temperature is lower than 32d, which makes the temperature lower than the downstream self-diagnosis resistor 32d. That is, when the resistance value of the upstream self-diagnosis resistor 32u is Ru3 and the resistance value of the downstream self-diagnosis resistor 32d is Rd3, Ru3 <Rd3. Therefore, a potential difference (V4> V3) is generated between the potential V3 at the inverting input terminal and the potential V4 at the non-inverting input terminal of the amplifier 34, and even when the flow rate is actually zero (engine stop), the flow rate is not equal to 0. Can produce a state of When the engine is operated, the potential difference (V4−V3) is necessarily increased with respect to the stop time.

  Therefore, by measuring the output of the external output terminal 16b during the second period t2 (measurement B shown in FIG. 3), the flow rate ≠ 0 can be measured.

  Since the normal operation (flow rate detection) is completed when the second period t2 ends, the switch 24 is connected to the terminal 24a (connection point 28a) by the switch control circuit 51 as in the second period t2, and the switch 33 is , Connected to the terminal 33a (connection point 36).

  Then, by taking the difference between the outputs obtained by the two measurements A and B, it is possible to determine whether the circuit of the heating resistance flow sensor 10 is normal or abnormal (self-diagnosis).

  In the present embodiment, the output of measurement A is, for example, 0 V (volts) if there is no abnormality. On the other hand, the output of measurement B is, for example, 1 V (volts) when the engine is stopped and 3 V when the engine is rotated if there is no abnormality. Therefore, a determination threshold is set between the output of measurement A (0 V) and the output of measurement B when the engine is stopped (1 V), and the value (difference) obtained by subtracting the output of measurement A from the output of measurement B is the above determination. If it is equal to or greater than the threshold, it is determined to be normal, and if it is less than the determination threshold, it can be determined to be abnormal. Possible causes of the abnormality include, for example, damage to the membrane 61 and short circuit.

  Also, when the upper limit judgment threshold is set by adding a margin to the maximum value that can be taken by the output of measurement B during engine rotation under normal conditions, and the output difference (measurement B-measurement A) exceeds the threshold Alternatively, it may be determined as abnormal.

  In this embodiment, since the self-diagnosis is performed immediately after the ignition key is turned on, the engine is in an idling state. Therefore, the upper limit determination threshold value may be set by adding a margin to the output of measurement B during idling (predetermined rotation speed (intake amount)) in a normal state.

  Thus, according to the heating resistance type flow sensor 10 and the self-diagnosis method according to the present embodiment, whether the engine is rotating or stopped, that is, whether the fluid is flowing or not flowing, Self-diagnosis can be performed.

  Further, in the present embodiment, the power-on reset circuit 50 and the switch control circuit 51 are triggered by power-on, and the state of the first period t1 and the state of the second period t2 that are necessary for self-diagnosis immediately after the power-on. Two different states can be set. Therefore, since a self-diagnosis terminal for inputting a self-diagnosis start signal is not required, the cost can be reduced accordingly. Moreover, the physique of the heating resistance type flow sensor 10 can also be reduced in size.

  In the upstream resistances 30u, 31u, and 32u and the downstream resistances 30d, 31d, and 32d that constitute the sensor unit 13, between the first upstream flow rate detection resistor 30u and the second upstream flow rate detection resistor 31u. A configuration in which an upstream self-diagnosis resistor 32u is provided and a downstream self-diagnosis resistor 32d is provided between the first downstream flow rate detection resistor 30d and the second downstream flow rate detection resistor 31d may be employed. A configuration in which the self-diagnosis resistors 32u and 32d are provided at positions closer to the heater resistor 11 than the flow rate detection resistors 30u, 30d, 31u, and 31d may be employed.

  However, as shown in the present embodiment, when the self-diagnosis resistors 32u and 32d used only during the self-diagnosis are provided at positions farthest from the heater resistor 11, the physique (fluid) of the sensor chip 60 compared to other configurations. Flow direction) can be reduced. Further, since the self-diagnosis resistors 32u and 32d are not located between the heater resistor 11 and the flow rate detection resistors 30u, 31u, 30d, and 31d, the influence of heat generated by the self-diagnosis resistors 32u and 32d is small when detecting the flow rate. The flow rate detection accuracy can be improved compared to other configurations.

  Also, when the power-on reset signal is input, the switch control circuit 51 controls the switches 24 and 33 so that the second period t2 is first, and then switches the switches 24 and 33 so that the first period t1 is reached. A control configuration can also be employed.

  However, as shown in the present embodiment, the switch control circuit 51 first controls the switches 24 and 33 so as to be in the state of the first period t1 in which the heater resistor 11 does not generate heat, and the first period t1 ends. When the two switches 24 and 33 are controlled so as to be in the state of the second period t2 continuously after the period t1, the waiting time for the temperature of the substrate 60 to drop is unnecessary as in the configuration in which the second period t2 is performed first. Therefore, the self-diagnosis time can be shortened.

  In the present embodiment, the first period t1 and the second period t2 are continuously executed from the start of operation after the power-on reset signal is input. However, the first period t1 and the second period t2 may be executed after a predetermined time has elapsed after the power-on reset signal is input. Alternatively, the second period t2 may be executed after a predetermined time has elapsed after the first period t1 ends.

(Modification)
In the present embodiment, in order to create a state in which no current flows through the heater resistor 11 in the first period t1 of the self-diagnosis, the fixed resistor on the side heat resistor 20 side that constitutes the bridge circuit 27 of the heater drive unit 12 is divided. In this example, two first fixed resistors 21a and 21b are used, and a connection point connected to the inverting input terminal of the amplifier 25 by the switch 24 is a connection point 28b between the first fixed resistors 21a and 21b. However, for example, as shown in FIG. 4, a switch 80 is provided between the transistor 26 and the heater resistor 11, and the switch 80 is turned off in response to an instruction signal from the switch control circuit 51 in the first period t <b> 1. No current may flow through 11. In this case, the switch 80 is turned on during the second period t2 and normal operation (flow rate detection).

  In FIG. 4, the half bridge on the side heat resistance 20 side constituting the bridge circuit 27 is formed by connecting the side heat resistance 20 and one first fixed resistance 21 in series, and the side heat resistance 20 and the first fixed resistance 21 are connected. A connection point 28 of the resistor 21 is connected to the inverting input terminal of the amplifier 25. In such a configuration, when the resistance value of the indirectly heated resistor 20 is Ri, the resistance value of the intake air temperature measuring resistor 22 is Rk, the resistance value of the fixed resistor 21 is R1, and the resistance value of the fixed resistor 23 is R2, the non-energized state R1 and R2 are set (for example, R1 = R2) so that Rk> Ri at the same temperature and V2> V1 immediately after the power is turned on.

  The switch 80 is not limited to between the transistor 26 and the heater resistor 11. For example, it may be provided between the transistor 26 and the heater resistor 11 or may be provided between the amplifier 25 and the transistor 26.

  However, as in the first embodiment (see FIG. 1), the first fixed resistor 21 is divided into two first fixed resistors 21a and 21b, and the connection points 28a and 28b are switched by the switch 24. Rather than providing a switch 80 between the terminal 16a and the heater resistor 11, the size of the switch can be reduced.

(Second Embodiment)
In the first embodiment, an example has been described in which the self-diagnostic circuit unit 15 creates the states of the first period t1 and the second period t2 using the power supply to the power supply terminal 16a as a trigger. On the other hand, the heating resistance type flow sensor 10 shown in FIG. 5 has a self-diagnosis terminal 16e as an external terminal, and by inputting a self-diagnosis instruction signal through the self-diagnosis terminal 16e, the switches 24, 33 is controlled. In addition, it is the same as 1st Embodiment (refer FIG. 1) except having the terminal 16e for self-diagnosis instead of the self-diagnosis circuit part 15. FIG.

  By adopting such a configuration, it is possible to achieve other effects other than the effect of eliminating the self-diagnosis terminal 16e among the effects shown in the first embodiment.

  In FIG. 5, the self-diagnosis terminal 16e is combined with the configuration shown in the first embodiment (see FIG. 1), but the self-diagnosis terminal 16e may be combined with the configuration shown in FIG.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  Although an example in which an npn-type bipolar transistor is employed as the transistor 26 has been shown, an n-channel MOSFET or IGBT can also be employed.

  The transistor 26 may be a pnp bipolar transistor, a p-channel MOSFET, or an IGBT. In this case, the connection points 28, 28 a and 28 b of the heater driving unit 12 may be connected to the non-inverting input terminal of the amplifier 25 and the connection point 29 may be connected to the inverting input terminal of the amplifier 25.

  Further, a configuration in which the indirectly heated resistor 20, the intake air temperature measuring resistor 22, and the fixed resistors 21 (21a, 21b) and 23 have negative temperature coefficients can be employed. Similarly, it is possible to adopt a configuration in which the resistors 30u, 30d, 31u, 31d, 32u, and 32d constituting the sensor unit 13 have a negative temperature coefficient.

  In this embodiment, the heater drive part 12 showed the example which has the side heat resistance 20. FIG. However, the present invention can also be applied to a known configuration in which the heater resistor 11 also serves as the side heat resistor 20.

  In this embodiment, the example which outputs the output of the amplifier 34 from the external output terminal 16b via the signal processing circuit unit 14 was shown. However, the signal processing circuit unit 14 may not be provided, and the output of the amplifier 34 may be output from the external output terminal 16b.

DESCRIPTION OF SYMBOLS 10 ... Heat generation resistance type flow sensor 11 ... Heater resistance 12 ... Heater drive part 15 ... Self-diagnosis circuit part (self-diagnosis means)
20 ... indirectly heated resistors 21a, 21b ... first fixed resistor 24 ... switch (second selection means)
25 ... Amplifier (second differential amplifier)
30u, 30d ... first flow rate detection resistors 31u, 31d ... second flow rate detection resistors 32u, 32d ... self-diagnosis resistors 33 ... switch (first selection means)
34 ... Amplifier (first differential amplifier)
38 ... Bridge circuit (first bridge circuit)
39 ... Bridge circuit (second bridge circuit)
50 ... Power-on reset circuit 51 ... Switch control circuit (selection means control circuit)

Claims (10)

A heater resistor (11) formed on the substrate (60) and generating heat when energized;
A heater drive unit (12) for controlling the energization state of the heater resistor (11);
Two first flow rate detection resistors (30u, 30d) which are formed on the substrate (60) in the same pattern using the same material, and are equidistant from the heater resistor (11) on the upstream side and the downstream side. ) Are connected in series with each other, the first flow rate detection resistor pair (30),
The heater resistance is formed on the substrate (60) in the same pattern using the same material as the first flow rate detection resistor (30u, 30d) and at a different distance from the first flow rate detection resistor (30u, 30d). Two second flow rate detection resistors (31u, 31d) positioned equidistantly on the upstream side and the downstream side with respect to (11) are connected in series to each other, and the first flow rate detection resistor pair (30) A second flow rate detection resistor pair (31) connected in parallel to each other;
An external output terminal (16b),
During normal operation for detecting the flow rate of the fluid, a signal based on the output of the first bridge circuit (38) configured by the two flow rate detection resistor pairs (30, 31) is sent via the external output terminal (16b). A heating resistance flow sensor (10) that outputs to the outside,
The same material as that of the flow rate detection resistors (30u, 30d, 31u, 31d) is formed on the substrate (60) in the same pattern, and the upstream and downstream sides of the heater resistor (11) are different from each other. Two self-diagnostic resistors (32u, 32d) located in a line are connected to each other in series, and the self-diagnostic resistor pair (32) is connected in parallel to the two flow rate detecting resistor pairs (30, 31). ,
Of the three resistance pairs (30, 31, 32), the first bridge circuit (38) constituted by the two flow rate detection resistance pairs (30, 31) and the first flow rate detection resistance pair. (30) and first selection means (33) for selectively connecting any one of the second bridge circuits (39) constituted by the self-diagnosis resistor pair (32) to the external output terminal (16b); With
In a predetermined first period (t1) that does not overlap with that during the normal operation, the heater drive unit (12) cuts off the power supply to the heater resistor (11) and the first selection means (33). The first bridge circuit (38) is connected to the external output terminal (16b);
During the normal operation and in a second period (t2) that does not overlap with the first period, power is supplied to the heater resistor (11) by the heater driving section (12), and the first selection means (33). The heating resistor type flow sensor, wherein the second bridge circuit (39) is connected to the external output terminal (16b). A connection point (35) of the first flow rate detection resistor (30u, 30d) is connected to one of input terminals, and a first differential amplifier (output terminal is electrically connected to the external output terminal (16b)). 34)
The first selection means (33) connects the connection point (36) of the second flow rate detection resistor (31u, 31d) during the normal operation and the first period (t1) to the first differential amplifier ( 34), and in the second period (t2), the connection point (37) of the self-diagnosis resistor (32u, 32d) is connected to the input terminal of the first differential amplifier (34). The heating resistance flow sensor according to claim 1, wherein: The heater driving unit (12)
Two first fixed resistors (21a, 21b) formed on the substrate (60) and connected in series to each other are formed on the substrate (60) and receive the heat of the heater resistor (11) to have a resistance value. A variable side heat resistance (20) connected in series is formed on the substrate (60), and is formed on the substrate (60), a fluid temperature measurement resistor (22) whose resistance value varies depending on the temperature of the fluid, and the substrate (60). A third bridge circuit (27) in which a second fixed resistor (23) is connected in series;
A connection point (29) of the fluid temperature measurement resistor (22) and the second fixed resistor (23) is connected to one input end, and the side heat resistance (20) and the first fixed resistor are connected to the other input end. A second differential amplifier (25) to which a connection point (28a) of the resistor (21a) or a connection point (28b) between the two first fixed resistors (21a, 21b) is connected;
Second selection means (24) for selectively connecting one of the two connection points (28a, 28b) to an input terminal of the second differential amplifier (25);
A transistor (26) connected to the output terminal of the second differential amplifier (25) and controlling the energization state of the heater resistor (11) based on the output of the second differential amplifier (25); Prepared,
The second selection means (24) inputs a connection point (28b) between the two first fixed resistors (21a, 21b) to the input of the second differential amplifier (25) in the first period (t1). In the normal operation and in the second period (t2), a connection point (28a) between the indirectly heated resistor (20) and the first fixed resistor (21a) is connected to the second differential amplifier ( The heating resistance type flow rate sensor according to claim 1 or 2, wherein the heating resistance type flow rate sensor is connected to an input terminal of 25). As self-diagnosis means (15),
A power-on reset circuit connected to a power supply line from the power supply terminal (16a) to the transistor (26) and outputting a power-on reset signal for initializing the circuit when the power supply terminal (16a) is turned on. (50),
In the first period (t1) based on the power-on reset signal, the first selection unit (33) sets the connection point (36) of the second flow rate detection resistor (31u, 31d) to the first difference. The second selection means (24) connects the connection point (28b) of the first fixed resistor (21a, 21b) to the input terminal of the dynamic amplifier (34), and the second differential amplifier (25). Connect to the input end
In the second period (t2) based on the power-on reset signal, the first selection means (33) sets the connection point (37) of the self-diagnosis resistors (32u, 32d) to the first differential amplifier. The second selection means (24) connects the connection point (28a) between the first fixed resistor (21a) and the indirectly heated resistor (20) to the second differential amplifier (34) while being connected to the input terminal of (34). 25) so that it connects to the input terminal
The heating resistance flow sensor according to claim 3, further comprising a selection means control circuit (51) for controlling the two selection means (24, 33).   When the power-on reset signal is input, the selection means control circuit (51) controls the two selection means (24, 33) to the state of the first period (t1), and the first period ( 5. The two selection means (24, 33) are controlled to the state of the second period (t 2) continuously with the first period (t 1) when t 1) ends. Heating resistance type flow sensor.   The self-diagnosis resistors (32u, 32d) are farther from the heater resistor (11) than the first flow rate detection resistors (30u, 30d) and the second flow rate detection resistors (31u, 31d). The heating resistance type flow rate sensor according to claim 1, wherein the heating resistance type flow rate sensor is formed at a position.   The self-diagnosis resistors (32u, 32d) are formed between the first flow rate detection resistors (30u, 30d) and the second flow rate detection resistors (31u, 31d). The heating resistance type flow sensor according to any one of claims 1 to 5.   The self-diagnosis resistor (32u, 32d) is closer to the heater resistor (11) than the first flow rate detection resistor (30u, 30d) and the second flow rate detection resistor (31u, 31d). The heating resistance type flow rate sensor according to claim 1, wherein the heating resistance type flow rate sensor is formed at a position. A self-diagnosis terminal (16e) is provided.
Based on a self-diagnosis instruction signal input from the outside via the self-diagnosis terminal (16e),
In the first period (t1), the heater drive section (12) cuts off the power supply to the heater resistor (11) and the first selection circuit (33) causes the first bridge circuit (38). Is connected to the external output terminal (16b),
In the second period (t2), electric power is supplied to the heater resistor (11) by the heater driving unit (12), and the second bridge circuit (39) is supplied by the first selection unit (33). The heating resistance flow sensor according to claim 1, wherein the flow sensor is connected to an external output terminal (16b).   The heating resistance flow sensor (10) according to any one of claims 1 to 9, wherein the output of the external output terminal (16b) in the first period (t1) and the external output in the second period (t2). A self-diagnosis method for a heating resistance flow sensor, characterized in that self-diagnosis is performed based on a difference in output of the terminal (16b).

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